There are other areas of temperature questions I want to point out here, or things we need to learn much more about.

Boreholes: Boreholes are narrow shafts bored down into the ground, in many cases to find water or gases. These are an excellent place to measure surface temperature changes because rocks effect the flow of heat making them ideal for measuring short term temperatures as the rocks smooth temperature changes out.

To accurately measure surface temperature changes we really need many more boreholes worldwide. It would be nice to see a worldwide borehole program.

In any case AR4 points out that geothermal reconstructions that have been made with public data showing “somewhat muted estimates” as half the boreholes have yet to see any “significant warming” in the last 20 years. They state they need more boreholes above 60 degrees North. (AR4 Section 6.6.1.2 Page 474)

Atmosphere: They note since 1950s the troposphere has warmed at a slightly faster rate than the surface, while the stratosphere “has cooled markedly since 1979.” (AR4 FAQ 3.1 Page 252)

AR4 produced evidence the troposphere had warming faster than the GMST (global mean surface temperature) and the stratosphere was cooling, but in AR5 the IPCC claims new satellites data has put these past observations in doubt. This is a big area of question today. (AR5 Section 2.4.4 Page 194) 

The IPCC in AR5 explains there are questions about the components of the radiation budget of the earth’s surface as they “cannot be directly measured by passive satellites”, it is easier for them to look at the TOA (top of atmosphere). (AR5 Section 2.3.1 Page 181)

Non-radiative, Radiative energy fluxes, Thermal radiation, and Surface radiation: The non-radiative surface energy balance components consist of things like rain, latent and sensible heat, subsurface water, as well as thermal radiative (shortwave and longwave) energy fluxes. I have seen studies that automatic weather station sites in Greenland on average see nonradiative energy fluxes contributed over 70% of daily melt energy in Greenland.

IPCC notes since AR4 better tools have improved the understanding of the magnitude of radiative energy fluxes. As a result, they have “update of the global annual mean energy balance diagram (Figure 2.11). There was no other update mentioned in AR5 for this. (AR5 Section 2.3.1 Page 181)

The IPCC has included new studies in AR5 on thermal radiation (longwave) measurements that became available in the 1990s. This is important area to understand as thermal radiation is sensitive to changes in greenhouse gases. (AR5 Section 2.3.3.2 Page 184)

With current limits of satellites to directly measure surface radiation the IPCC notes another important issue is that there is limited data of surface net radiation measurements because of the lack of measuring locations. (AR5 Section 2.3.3.2 Page 185)

TCR and ECS: Next, I want to mention questions around transient climate response (TCR) and equilibrium climate sensitivity (ECS).

These are useful metrics to sum up the global climate’s temperature response to external RF. Both have to do with idea of a temperature change from the doubling of the CO2. ECS is the change in annual mean GMST (global mean surface temperature) once the climate system reached equilibrium, taking time, compared to TCR which is the change in annual mean GMST over just the last 70 years.

The IPCC explains “Neglecting important sources of uncertainty in these estimates will result in overly narrow ranges that overstate the certainty with which the ECS or TCR is known”. (AR4 Section 9.6.4 Page 725)

They go on to state their “confidence is increased by the similarities between individual ECS estimates”. (AR4 Section 9.6.4 Page 726)

Solar Cycle: Last, I want to mention a current issue the IPCC discovered in AR5, which is satellites indicate there was a larger than expected reduction in ultraviolet wavelengths during last declining of the solar cycle.

They explain “Changes in solar UV drive stratospheric O3 chemistry and can change RF.” They go on “expected to alter estimates of the maximum absolute magnitude of the solar contribution to RF” believing their range still holds. They note some studies show there may be regional impacts. (AR5 Section 11.3.6.2.2 Page 1007)

I look forward to the update in AR6 if solar UV drives stratospheric O3 chemistry possibly changing the overall value of RF.